The present invention relates to the field of conducting pressurized fluids in a plastic pipe, and more particularly to an apparatus for transporting natural gas from a source of supply to a delivery point.
Plastic pipe is now commonly being used for the underground transmission and delivery of fluids such as natural gas replacing the conventional steel pipe. The use of plastic pipe for the transmission of such fluids including natural gas, propane, butane, and others provides advantages of corrosion resistance, low cost, low weight, reliability, and flexibility but also requires specialized pipe connectors to connect to existing steel pipe fittings.
In the natural gas delivery field, plastic pipe is used to deliver gas from an underground gas main to an above ground gas meter for introduction into a building. However, safety and various government regulations require that any above ground portion of the plastic gas line be protected from possible damage or puncture. Thus, the above ground portion of the plastic pipe delivering the gas from the gas main to the gas meter is surrounded by a protective metallic pipe which also connects the plastic pipe to the gas meter. This metallic pipe must be secured around the plastic pipe in a gas tight manner.
A gas riser is used to connect an underground plastic gas delivery pipe to a gas meter. The gas riser is generally L-shaped in configuration and includes an outer metallic conduit or housing and an internal plastic pipe. The internal plastic pipe has an extended leg at a lower end which is adapted to be interconnected to an underground plastic pipe line using a plastic pipe sleeve coupling. At the upper end of the riser, a seal is provided between the inner plastic pipe and the surrounding metallic pipe to prevent gas from seeping into the annular space surrounding the internal plastic pipe. Threads on an upper end of the metallic outer pipe are adapted to engage a meter bar or meter manifold of a gas meter.
The seal between the metallic outer pipe and the plastic inner pipe is formed by providing one or more grooves on an exterior of the plastic pipe which each receive a sealing gasket, and crimping the metallic pipe at the location of each sealing gasket to form a seal. An example of such a sealing arrangement for a gas riser is shown in U.S. Pat. No. 3,987,820. However, with this gasket sealing arrangement expansion and contraction due to environmental temperature changes may compromise the seal between the metallic and plastic pipes allowing gas to escape into the environment.